The present invention relates to an automatic tool changing device for machining centers such as a numerical control milling machine with an automatic tool changing device. on of
Two principal types of such device are known in the art, namely, a turret head type, and an arm type in which the necessary tool changes are accomplished by means of an arm and tool transport unit, such as, a robot which is arranged between a tool magazine and the spindle of a machine tool. A disadvantage of the turret head type is that while the tool changing time is relatively short, the number of tools that can be held of the head is usually on the order of 6 to 8 tools thus making it unsuitable for use on machining centers designed to handle a wide range of machining operations, and moreover there is the disadvantage of causing indexing errors, misalignment and the like. The latter arm type is also disadvantageous in that since the tool holding head must first be raised to a predetermined height to permit the tool change by the robot and then the head must be lowered to permit the machining of the work, even in the case of a small-sized work, the head must be raised to such predetermined height thus requiring a dead time, waste time in changing the tools, unavoidably making the device large and complicated in construction and making it impossible to use this type of device on machining centers in view of the recent trend in designing toward smaller machining centers.